From 478c700c01cb041a95a4540915717c3012d1e5b2 Mon Sep 17 00:00:00 2001 From: Chinmay V S Date: Fri, 3 Feb 2012 21:30:50 +0530 Subject: Optimise apply_slack() for size and speed. To apply proper slack, the original algorithm used to prepare a mask and then apply the mask to obtain the appropriately rounded-off absolute time the timer expires. This patch modifies the masking logic to a bit-shift logic, therby reducing the complexity and number of operations. Thus obtaining a minor speed-up. Signed-off-by: Chinmay V S Signed-off-by: Stefan Guendhoer --- kernel/timer.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index f22f8ae13..f5bdb1b50 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -805,9 +805,7 @@ EXPORT_SYMBOL(mod_timer_pending); * Algorithm: * 1) calculate the maximum (absolute) time * 2) calculate the highest bit where the expires and new max are different - * 3) use this bit to make a mask - * 4) use the bitmask to round down the maximum time, so that all last - * bits are zeros + * 3) round down the maximum time, so that all the lower bits are zeros */ static inline unsigned long apply_slack(struct timer_list *timer, unsigned long expires) @@ -831,9 +829,8 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires) bit = find_last_bit(&mask, BITS_PER_LONG); - mask = (1UL << bit) - 1; - - expires_limit = expires_limit & ~(mask); + /* Round down by zero-ing the lower bits */ + expires_limit = (expires_limit >> bit) << bit; return expires_limit; } -- cgit v1.2.3